2008 Valves-Why do the clearances get smaller the more you ride?

By Boise93, Posted February 3, 2010

I'm nearing the 100 hour Vet Intermediate mark on my 2008, 450. When I recently checked the valves, the clearances were slightly (.001+-) tighter than 15 hours ago. I keep excellent maintenance on my bike, change my oil after every 3 hours, and I'm not banging it against the rev limiter.

So my question is, why do the valve clearances get smaller the more you ride. Wouldn't logic make the valves deteriorate the more your ride, thus making the clearances get larger eventually? What concept am I missing, am I over-thinking this?

Gray, any help?

By KJ790, Posted February 3, 2010

As the valve and the valve seat wear, the valve sits deeper in the seat, thus moving up towards the cam. Since the valve clearance is essentially the space between the valve and cam, this space gets smaller as the valve gets worn.

By KJ790, Posted February 3, 2010

the valves stretch

No they don't, the face of the valve and the valve seat wears.

By mkporn, Posted February 3, 2010

No they don't, the face of the valve and the valve seat wears.

What he said. They don't stretch, the valve actually starts beating into the seat after the hard facing wears (the non hard faced Ti is actually pretty soft compared to the hard face they put on the valve)...once the hard facing goes away the valve goes pretty quick, that is why you can ride it for a 100hr without a problem then the valves tighten a bit and the next thing you know 10hrs later they need to be adjusted again.

By grayracer513, Posted February 3, 2010

the valves stretch

Not in a YZF, they don't.

By KJ790, Posted February 4, 2010

Not in a YZF, they don't.

Hopefully not in any engine. If your valves are measurably stretching, your engine is milliseconds seconds away from self destruction...

By grayracer513, Posted February 4, 2010

Hopefully not in any engine. If your valves are measurably stretching, your engine is milliseconds seconds away from self destruction...

Another old time legend brought along from the last century. Fifty years ago or better, car engines, especially circle car engines and such that were subjected to long stretches of time at extremely heavy loads would sometimes get the exhaust valves so hot that the valve heads would deform and the center would be pulled into the port. This was called "tuliping", and it was never really a matter of any part of the valve elastically stretching, but the valve did get longer for it. Occasionally, someone would take too much weight off of their intake valve heads, and this would happen to them as well.

But contemporary materials have, for the most part, resigned such failures to history. Besides, the YZF doesn't have valve springs strong enough to do this, even if it had mild steel valves.

By SC162, Posted March 24, 2012

I'm nearing the 100 hour Vet Intermediate mark on my 2008, 450. When I recently checked the valves, the clearances were slightly (.001+-) tighter than 15 hours ago. I keep excellent maintenance on my bike, change my oil after every 3 hours, and I'm not banging it against the rev limiter.

So my question is, why do the valve clearances get smaller the more you ride. Wouldn't logic make the valves deteriorate the more your ride, thus making the clearances get larger eventually? What concept am I missing, am I over-thinking this?

Gray, any help?

I have been thinking the same thing and after googling and searching on here i still dont understand it

As the valve and the valve seat wear, the valve sits deeper in the seat, thus moving up towards the cam. Since the valve clearance is essentially the space between the valve and cam, this space gets smaller as the valve gets worn.

I would have thought the further they sat into the seat, the further they would move away from the cam, meaning the larger the gap? What am i missing?

I only ask because I want to learn about and understand these 4t motors before i attempt to work on it lol

By Gunner354, Posted March 24, 2012

I have been thinking the same thing and after googling and searching on here i still dont understand it

I would have thought the further they sat into the seat, the further they would move away from the cam, meaning the larger the gap? What am i missing?

I only ask because I want to learn about and understand these 4t motors before i attempt to work on it lol

No offense, but you need to understand this basic concept before you work on the motor.

Edited March 24, 2012 by Gunner354

By crf450319, Posted March 24, 2012

This might help you understand... the backside of the valve wears, and as a result there's less material keeping the entire valve deeper into the head. The more the backside of the valve wears, the closer the valve gets to the cam - so, more wear equals less clearance.

Here's a pic of on of my old intake valves from my Honda, you'll notice the area circled in red and how that would cause the valve to move closer to the cam. I also drew a really nice picture... let me know if this helps you understand why valve wear means tighter clearance(s).

When you are checking valve clearance, you are essentially checking the space between the top of the valve and the cam. The more the valve wears and gets "cupped" out, the closer the valve moves towards the cam and the less clearance you'll have.

Edited March 24, 2012 by crf450319

By grayracer513, Posted March 24, 2012

...i still dont understand it

I would have thought the further they sat into the seat, the further they would move away from the cam, meaning the larger the gap? What am i missing?

If you could reach into an assembled head and pull the valve down off the seat, the top of the stem would be pulled down farther away from the cam, would it not? Then, if you release it, the valve will move closer to the cam until it hits the seat, right? Then if the face of the valve or the face of the seat wear away, the stem will move closer to the cam, not farther away.

By highmarker, Posted March 24, 2012

sometimes you'll see exh clearances get looser if the valve and seat are growing deposits, not usually on these motors though

By SC162, Posted March 24, 2012

This might help you understand... the backside of the valve wears, and as a result there's less material keeping the entire valve deeper into the head. The more the backside of the valve wears, the closer the valve gets to the cam - so, more wear equals less clearance.

Here's a pic of on of my old intake valves from my Honda, you'll notice the area circled in red and how that would cause the valve to move closer to the cam. I also drew a really nice picture... let me know if this helps you understand why valve wear means tighter clearance(s).

When you are checking valve clearance, you are essentially checking the space between the top of the valve and the cam. The more the valve wears and gets "cupped" out, the closer the valve moves towards the cam and the less clearance you'll have.

Perfectly explained. I had no idea they came back up into the seat, i thought the seat was under the valve, but now it makes sense (rookie i know haha). Thankyou

And yes i know i need to understand it better, being the reason i asked. This is my first 4T, having only ever owned 2T's before. Not as though i would attempt to change valves or anything like. Our bikes have just had some trouble with the intakes closing up and instead of taking it back to a dealer i am gunna check em before i ride it next and then after the ride to make sure they arent moving too quickly, and just wanted to understand the basic principle behind it all. Thanks for your help

Edit: also everyone keeps saying the face of the valve wears which causes it to move, which i took as meaning the face closest to the piston. I assumed it was this face that hit the seat, if u know what i mean

Edited March 24, 2012 by SC162

By grayracer513, Posted March 24, 2012

See if this helps your understanding of it:

By crf450319, Posted March 25, 2012

Perfectly explained. I had no idea they came back up into the seat, i thought the seat was under the valve, but now it makes sense (rookie i know haha). Thankyou

And yes i know i need to understand it better, being the reason i asked. This is my first 4T, having only ever owned 2T's before. Not as though i would attempt to change valves or anything like. Our bikes have just had some trouble with the intakes closing up and instead of taking it back to a dealer i am gunna check em before i ride it next and then after the ride to make sure they arent moving too quickly, and just wanted to understand the basic principle behind it all. Thanks for your help

Edit: also everyone keeps saying the face of the valve wears which causes it to move, which i took as meaning the face closest to the piston. I assumed it was this face that hit the seat, if u know what i mean

No problem at all, I am a visual learner and I can understand how it would be difficult to figure out by reading text alone. Glad we could help !